This invention relates to a process for catalytic conversion of hydrocarbon feedstock in the absence of added hydrogen. More particularly, the present invention relates to a catalytic conversion process for producing isobutane and isoparaffin-enriched gasoline.
The mixture of isoparaffins possessing high octane number, low octane sensitivity, appropriate volatility and clean burning is an ideal blending components for aviation gasoline and motor gasoline. The mixture of isoparaffins can be obtained by propylene polymerization or alkylation reaction of isobutane and olefins.
The conventional fluidized catalytic cracking (FCC) technology is used for producing gasoline with a yield of up to 50 wt %. In the 1980s, the phase down of leaded gasoline forced the catalytic cracking technology to go forward to the production of high octane gasoline. The changing market demands have resulted in a great change in technology and catalyst types. The advance in technological development is to increase reaction temperature, shorten reaction time, intensify reaction severity, suppress hydrogen transfer reaction and overcracking reaction and improve the contacting efficiency between feedstock and hot catalyst at the bottom of a riser reactor. In catalyst development, the catalysts containing USY zeolite supported on an inert or active matrix or containing different typed zeolites have been put into commercial use.
Though FCC technology has been advanced to meet octane blending requirement, whether it is by means of changing in process parameters or using novel catalysts for increasing gasoline octane number, it results in an increase in olefin content of FCC gasoline. Apparently, there is a great difference between the olefin contents of about 35 wt %xcx9c65 wt % in FCC gasoline and that required for reformulated gasoline (RFG). FCC liquid petroleum gas (LPG) has an olefin content of up to 70 wt %, in which butylenes is several times as much as the yield of isobutane, so it is not fit to be used as feedstock for alkylation.
U.S. Pat. No. 5,154,818 discloses a method for the fluidized catalytic cracking of plural hydrocarbon feedstocks in a riser reactor to produce more gasoline of high octane number. The process generally comprises two reaction zones. A relatively light hydrocarbon feedstock contacts with spent catalyst in a first reaction zone located in the bottom of a conventional riser where aromatization and oligomerization take place. All of the first reaction zone effluent, the regenerated catalyst and heavy hydrocarbon feedstock are introduced into the second reaction zone where heavy hydrocarbon feedstock is cracked to desired reaction products. The reaction products and spent catalyst then pass through disengager for removal of entrained catalyst before the hydrocarbon vapors pass into a separation system. Spent catalyst passes into stripper and is divided into two parts, one is introduced into regenerator for burning off coke, the other part is recycled to the first reaction zone.
U.S. Pat. No. 4,090,948 discloses a catalytic cracking process for producing the desired conversion of hydrocarbon feedstock of inferior quality (having higher contents of basic nitrogen and carbon residue) to obtain higher yields of the desired products in a riser reactor. The process generally comprises contacting the hydrocarbon feedstock containing the highly reactive nitrogen and carbon residue with a recycled spent catalyst in the first reaction zone where the highly reactive nitrogen and carbon residue will deposit on the spent catalyst and then contacting the resultant mixture with freshly regenerated catalyst in the second reaction zone. The reaction products and spent catalyst then pass through disengager for removal of entrained catalyst before the hydrocarbon vapors pass into a separation system. Spent catalyst passes into stripper and is divided into two parts, one is introduced into regenerator for burning off coke and then returned to the second reaction zone, and the other part is recycled without regeneration to the first reaction zone.
Though the above two prior art processes have divided an iso-diameter riser reactor into two reaction zones, the reactions take place at lower temperature in the first reaction zone and the reactions take place at higher temperature in the second reaction zone. In addition, the processes utilize a conventional riser reactor without flexibility for adjusting operating conditions. This arrangement is subject to significant disadvantages to carry on catalytic cracking reaction and selective hydrogen transfer at the same time for producing LPG with higher yield of isobutane and isoparaffin enriched gasoline.
An object of the present invention is to provide a catalytic conversion process for producing isobutane and isoparaffin-enriched gasoline to meet the requirement for blending components of the RFG, i.e., limiting the olefin content on the premise of maintaining higher gasoline octane number.
The process provided by the present invention is to contact the preheated hydrocarbon feedstock with hot regenerated catalyst in the lower part of a reactor with the result that hydrocarbon cracking reaction takes place at higher reaction temperature and shorter reaction time, and then the resultant mixture is up-flowed and enters into a suitable reaction environment with the result that isomerization and hydrogen transfer reaction take place at lower reaction temperature and longer reaction time. The reaction products and spent catalyst that pass through disengager for removal of entrained catalyst. The reaction products flow into subsequent separation system. Spent catalyst is stripped with steam, and then flow into the regenerator for regeneration, and thereafter the hot regenerated catalyst is recycled to the lower part of the reactor.
The process provided by the present invention employs a reactor to carry on two different reactions under different operating conditions, said reactor is preferably selected from the group consisting of an iso-diameter riser, an iso-linear velocity riser, a multi-cascade riser, a fluidized bed or a combination reactor of an iso-diameter riser and a fluidized bed.
The applicants have found that the olefins produced by catalytic cracking reaction can be selectively converted into isoparaffins and aromatics or isoparaffins and coke under specific reaction conditions and with specific catalysts.
The present invention is practiced by different embodiments. In embodiment one, the invention is a process comprising: the preheated hydrocarbon feedstock is atomized with injection steam and charged into the bottom of a conventional iso-diameter riser, and then mixed with hot regenerated catalyst with the result that feedstock is vaporized and cracked. The product vapors and the coke deposited catalyst are up-flowed and are mixed with cooled regenerated catalyst with the result that isomerization and hydrogen transfer reaction take place. The reaction vapors and catalyst flow into disengager where entrained catalyst is separated and dropped into the catalyst stripper. The reaction vapors are separated into products in subsequent separation system. Spent catalyst is stripped and introduced into regenerator for regeneration. Regenerated catalyst is divided into two parts, one is recycled into the prelift zone of the riser, and the other part is cooled in catalyst cooler and then recycled into the second reaction zone.
In embodiment two, this invention is a process comprising: the preheated hydrocarbon feedstock is atomized with injection steam and charged into the bottom of a convention iso-diameter riser, and then mixed with hot regenerated catalyst with the result that the feedstock is vaporized and cracked. The product vapors and the coke deposited catalyst are up-flowed and are mixed with cooled semi-regenerated catalyst with the result that isomerization and hydrogen transfer reaction take place. The reaction vapors and catalyst flow into disengager where entrained catalyst is separated and dropped into the catalyst stripper. The reaction vapors are separated into products in subsequent separation system. Spent catalyst is stripped and introduced into the primary regenerator for regeneration. Semi-regenerated catalyst is divided into two parts, one flows into the secondary regenerator for regeneration, and then is recycled into the prelift zone of the riser, and the other part is cooled in catalyst cooler and then recycled into the second reaction zone.
In embodiment three, this invention is a process comprising: the preheated hydrocarbon feedstock is atomized with injection steam and charged into the bottom of the riser in a combination reactor of an iso-diameter riser and a fluidized bed, and then mixed with hot regenerated catalyst with the result that the feedstock is vaporized and cracked. The product vapors and the coke deposited catalyst in the riser flow upward and are mixed with cooled regenerated catalyst with the result that isomerization and hydrogen transfer reaction take place in the fluidized bed. The reaction vapors and catalyst flow into disengager where entrained catalyst is separated and dropped into the catalyst stripper. The reaction vapors are separated into products in subsequent separation system. Spent catalyst is stripped and introduced into regenerator for regeneration. Regenerated catalyst is divided into two parts, one is recycled into the prelift zone of the riser, and the other part is cooled in catalyst cooler and then recycled into the fluidized bed.
In a more preferred embodiment of this invention, this invention comprises that the preheated hydrocarbon feedstock is atomized with injection steam and charged into the bottom of the first reaction zone in a multi-cascade riser, and then mixed with hot regenerated large particle size distribution catalyst containing USY zeolite with the result that feedstock is vaporized and cracked, providing the lifting force to carry the product vapors and the coke deposited catalyst in the first reaction zone into the second reaction zone where the effluents are mixed with the cooled regenerated small particle size distribution catalyst containing rare-earth Y zeolite with the result that isomerization and hydrogen transfer reaction take place. The reaction vapors and catalyst flow into disengager where entrained catalyst is separated and dropped into the catalyst stripper. The reaction vapors are separated into products in subsequent separation system. Spent catalyst is stripped and introduced into regenerator for regeneration. Regenerated catalyst is divided into the large particle size distribution catalyst and the small particle size distribution catalyst, the large particle size distribution catalyst is recycled into the prelift zone of the riser, and the small particle size distribution catalyst is cooled in catalyst cooler and then recycled into the second reaction zone.
The above embodiments are not meant to limit the present invention to the details disclosed herein.